Deck 22: Biosynthesis of Amino Acids, Nucleotides, and Related Molecules

Question 1

In which group are all the amino acids closely interrelated metabolically?

A) arginine, hydroxyproline, and histidine
B) arginine, tyrosine, and glutamate
C) glycine, valine, glutamine, and aspartate
D) ornithine, alanine, glycine, and valine
E) ornithine, proline, arginine, and glutamate

Answer 1

E

Question 2

An amino acid that does NOT derive its carbon skeleton, at least in part, from oxaloacetate is:

A) aspartate.
B) lysine.
C) methionine.
D) proline.
E) threonine.

Answer 2

D

Question 3

The nitrogen atom in the side chain of lysine is derived from which amino acid?

A) aspartic acid
B) glutamic acid
C) glutamine
D) asparagine
E) arginine

Answer 3

B

Question 4

Which enzyme is NOT involved in the assimilation of inorganic nitrogen into an organic molecule?

A) dinitrogenase reductase
B) nitrate reductase
C) nitrite reductase
D) nitrile reductase
E) dinitrogenase

Question 5

Which amino acid derives its nitrogen from a purine ring?

A) histidine
B) lysine
C) arginine
D) glutamine
E) tryptophan

Question 6

Which statement about the fixation of atmospheric nitrogen (N₂) into NH₃ by living cells is FALSE?

A) It involves the transfer of eight electrons per mol of N₂.
B) It occurs in certain microorganisms, but not in humans.
C) It requires a source of electrons, normally ferredoxin.
D) It requires one ATP per mol of N₂ fixed.
E) It requires two key protein components, each containing iron.

Question 7

Homoserine is:

A) a precursor of both methionine and threonine.
B) a precursor of serine.
C) derived from homocysteine.
D) derived from serine.
E) derived from threonine.

Question 8

Glutamine synthetase converts _____ to _____, whereas glutamate synthase converts _____ to _____.

A) formate; glutamine; ammonia; glutamate
B) asparagine; glutamine; $\alpha$ -ketoglutarate; glutamate
C) $\alpha$ -ketoglutarate; glutamine; oxaloacetic acid; glutamate
D) $\alpha$ -ketoglutarate; glutamine; $\alpha$ -ketoglutarate; glutamate
E) glutamate; glutamine; $\alpha$ -ketoglutarate; glutamate

Question 9

Glutamine, arginine, and proline:

A) do not have a common precursor.
B) may all be derived from a citric acid cycle intermediate.
C) may all be derived from a Cori cycle intermediate.
D) may all be derived from a glycolytic intermediate.
E) may all be derived from a urea cycle intermediate.

Question 10

If a cell were unable to synthesize or obtain tetrahydrofolic acid (H₄ folate), it would probably be deficient in the biosynthesis of:

A) isoleucine.
B) leucine.
C) lysine.
D) methionine.
E) serine.

Question 11

The nitrogen atom in the indole ring of tryptophan is derived from which amino acid?

A) aspartic acid
B) glutamic acid
C) glutamine
D) asparagine
E) arginine

Question 12

An important intermediate in the biosynthetic pathway to aromatic amino acids is:

A) benzoic acid.
B) lactate.
C) orotate.
D) shikimate.
E) $\alpha$ -ketoglutarate.

Question 13

An amino acid that does NOT derive its carbon skeleton, at least in part, from $\alpha$ -ketoglutarate is:

A) arginine.
B) glutamate.
C) glutamine.
D) proline.
E) threonine.

Question 14

If glucose labeled with ¹⁴C at C-1 were the starting material for amino acid biosynthesis, the product that would be readily formed is:

A) serine labeled at the carboxyl carbon.
B) serine labeled at alpha carbon.
C) serine labeled at the R-group carbon.
D) All of the answers are correct.
E) None of the answers is correct.

Question 15

Nonessential amino acids:

A) are amino acids other than those required for protein synthesis.
B) are not utilized in mammalian proteins.
C) are synthesized by plants and bacteria, but not by humans.
D) can be synthesized in humans as well as in bacteria.
E) may be substituted with other amino acids in proteins.

Question 16

The enzymatic machinery to fix atmospheric N₂ into NH₄⁺ is:

A) a means of producing ATP when excess N₂ is available.
B) composed of two key proteins, each containing iron.
C) relatively stable when exposed to O₂.
D) specific to plant cells.
E) unaffected by the supply of electrons.

Question 17

Which statement is NOT true about glutamine amidotransferases?

A) These enzymes proceed via a covalent intermediate.
B) Ammonia is released into a channel.
C) Glutamate is a product of the reaction.
D) ATP is needed to activate the glutamine.
E) A Cys at the active site is critical for the activity of these enzymes.

Question 18

Erythrose 4-phosphate is a precursor of:

A) aspartate.
B) cysteine.
C) phenylalanine.
D) serine.
E) threonine.

Question 19

Which enzyme is NOT involved in the assimilation of inorganic nitrogen into an organic molecule?

A) arginase
B) glutamate dehydrogenase
C) glutamate synthase
D) glutamine synthetase
E) dinitrogenase

Question 20

Which statement is NOT true about the anammox reaction?

A) Anammox converts ammonia to nitrogen.
B) Anammox is performed by symbiotic bacteria of leguminous plants.
C) Anammox generates the highly reactive molecule hydrazine that is a component of rocket fuel.
D) Anammox occursw anaerobically.
E) The ultimate electron acceptor in anammox is nitrite.

Question 21

The synthesis of purine and pyrimidine nucleotides differ in that:

A) ATP is required in the synthesis of purines but not in the synthesis of pyrimidines.
B) purine biosynthesis starts with the formation of PRPP, whereas pyrimidines incorporate the PRPP near the end of the pathway.
C) purine formation requires a THF derivative, whereas pyrimidine formation does not.
D) pyrimidine biosynthesis is tightly regulated in the cell, whereas purine biosynthesis is not.
E) pyrimidines go through many steps, adding a single carbon or nitrogen each time, whereas the basic skeleton for purines is formed by two main precursors.

Question 22

The MOST direct precursors of the nitrogens of UMP are:

A) aspartate and carbamoyl phosphate.
B) glutamate and aspartate.
C) glutamate and carbamoyl phosphate.
D) glutamine and aspartate.
E) glutamine and carbamoyl phosphate.

Question 23

The plant hormone indole-3-acetate (auxin) is formed from:

A) arginine.
B) histidine.
C) phenylalanine.
D) threonine.
E) tryptophan.

Question 24

The amino acid that gives rise to the biological messenger NO is:

A) glutamine.
B) arginine.
C) proline.
D) lysine.
E) histidine.

Question 25

Glutathione is a(n):

A) enzyme essential in the synthesis of glutamate.
B) isomer of oxidized glutamic acid.
C) methyl-group donor in many biosynthetic pathways.
D) product of glutamate and methionine.
E) tripeptide of glycine, glutamate, and cysteine.

Question 26

An intermediate of purine degradation in humans is:

A) glutamate.
B) NH₄⁺.
C) succinate.
D) urea.
E) uric acid.

Question 27

CMP, UMP, and TMP all have _____ as a common precursor.

A) adenosine
B) aspartate
C) glutamine
D) inosine
E) S-adenosyl methionine

Question 28

Which statement is TRUE of the biosynthetic pathway for purine nucleotides?

A) CO₂ does not participate in any of the steps in this pathway.
B) Deoxyribonucleotides are formed from 5-phosphodeoxyribosyl 1-pyrophosphate.
C) Inosinate is the purine nucleotide that is the precursor of both adenylate and guanylate.
D) Orotic acid is an essential precursor for purine nucleotides.
E) The amino acid valine is one of the precursors contributing to purine nucleotides.

Question 29

The hormones epinephrine and norepinephrine are derived biosynthetically from:

A) arginine.
B) histidine.
C) isoleucine.
D) tryptophan.
E) tyrosine.

Question 30

Bile pigments are:

A) formed in the degradation of heme.
B) generated by oxidation of sterols.
C) responsible for light reception in the vertebrate eye.
D) secreted from the pancreas
E) the products of purine degradation.

Question 31

Which statement CORRECTLY describes the biosynthetic pathway for purine nucleotides?

A) Purine deoxynucleotides are made by the same path as ribonucleotides, followed by reduction of the ribose moiety.
B) The first enzyme in the path is aspartate transcarbamoylase (ATCase).
C) The nitrogen in the purine base that is bonded to ribose in the nucleotide is derived originally from glycine.
D) The pathway occurs only in plants and bacteria, not in animals.
E) The purine rings are first synthesized, then condensed with ribose phosphate.

Question 32

The amino acid _____ and is an intermediate in the biosynthesis of _____.

A) histidine; purines
B) glycine; heme
C) serine; heme
D) serine; sphingosine
E) glutamine; glutathione

Question 33

Which statement is NOT true of the reaction catalyzed by ribonucleotide reductase?

A) Glutathione is part of the path of electron transfer.
B) It acts on nucleoside diphosphates.
C) Its mechanism involves formation of a free radical.
D) There is a separate enzyme for each nucleotide (ADP, CDP, GDP, UDP).
E) Thioredoxin acts as an essential electron carrier.

Question 34

L-Dopa is an intermediate in the conversion of:

A) phenylalanine to homogentisic acid.
B) phenylalanine to tyrosine.
C) tyrosine to epinephrine.
D) tyrosine to phenylalanine.
E) tyrosine to phenylpyruvate.

Question 35

The ribosyl phosphate moiety needed for the synthesis of orotidylate, inosinate, and guanylate is provided MOST directly by:

A) 5-phosphoribosyl 1-pyrophosphate.
B) adenosine 5'-phosphate.
C) guanosine 5'-phosphate.
D) ribose 5-phosphate.
E) ribulose 5-phosphate.

Question 36

Glutamine is a nitrogen donor in the synthesis of:

A) CTP.
B) dTTP.
C) inosinic acid (IMP).
D) orotate.
E) UMP.

Question 37

Precursors for the biosynthesis of the pyrimidine ring system include:

A) carbamoyl phosphate and aspartate.
B) glutamate, NH₃, and CO₂.
C) glycine and succinyl-CoA.
D) glycine, glutamine, CO₂, and aspartate.
E) inosine and aspartate.

Question 38

Orotic aciduria is an inherited metabolic disease in which orotic acid (orotate) accumulates in the tissues, blood, and urine. The metabolic pathway in which the enzyme defect occurs is:

A) epinephrine synthesis.
B) purine breakdown.
C) purine synthesis.
D) pyrimidine breakdown.
E) pyrimidine synthesis.

Question 39

A cell that is unable to synthesize or obtain tetrahydrofolic acid (H₄ folate) would probably be deficient in the biosynthesis of:

A) CMP.
B) GMP.
C) orotate.
D) thymidylate (TMP).
E) UMP.

Question 40

De novo purine biosynthesis is distinguished from de novo pyrimidine biosynthesis by:

A) condensation of the completed purine ring with ribose phosphate
B) incorporation of CO₂.
C) inhibition by azaserine (a glutamine analog).
D) participation of aspartate.
E) participation of PRPP (phosphoribosyl pyrophosphate).

Question 41

Which molecule is NOT a high-energy molecule involved in the synthesis of arginine from glutamate?

A) Acetyl-CoA
B) ATP
C) NADH/NADPH
D) FADH₂
E) All of these molecules are involved in this pathway.

Question 42

Which kind of reversible covalent modification is used to regulate glutamine synthetase?

A) ADP-ribosylation
B) adenylylation
C) phosphorylation
D) acetylation
E) both ADP-ribosylation and adenylylation

Question 43

The bacteria A. vinelandii uncouples oxidative phosphorylation during nitrogen fixation for what reason?

A) It increases the temperature so that the enzymes will function at maximum efficiency.
B) It ensures that the citric acid cycle is fully active and providing substrates for nitrogen fixation.
C) It ensures that ATP is not present to inhibit nitrogen fixation.
D) It maintains a low level of reduced cofactors.
E) It ensures that oxygen concentrations are kept low to prevent interference with enzymes.

Question 44

Which amino acid is NOT considered to originate from $\alpha$ -ketoglutarate?

A) arginine
B) glutamate
C) glutamine
D) histidine
E) proline

Question 45

Which statement is FALSE regarding the synthesis of glycine from 3-phosphoglycerate (3PG)?

A) Oxidation of 3PG creates an $\alpha$ -keto acid.
B) Pyridoxal phosphate is a required cofactor for this process.
C) The uncommon amino acid phosphoserine is an intermediate in the process.
D) A dehydration reaction produces glycine from serine.
E) A phosphatase catalyzes one of the reaction steps.

Question 46

Which statement is FALSE regarding glutamine synthetase?

A) Both the Type I and Type II forms have dihedral symmetry.
B) Histidine, glycine, and alanine are all negative effectors for this enzyme.
C) It is regulated by multiple feedback inhibitors and covalent modification.
D) ATP is an inhibitor for this enzyme.
E) This enzyme is classified as a ligase.

Question 47

Which statement is TRUE about gout?

A) Gout is caused by excessive breakdown of pyrimidine nucleotides.
B) Gout can be treated by administration of fluorouracil.
C) Gout is particularly prevalent in patients lacking xanthine oxidase.
D) Gout leads to deposition of sodium urate crystals in the joints.
E) Eating more liver is an effective way to treat the symptoms of gout.

Question 48

The synthesis of methionine originates from which compound?

A) $\alpha$ -ketoglutarate
B) 3-phosphoglycerate
C) oxaloacetate
D) pyruvate
E) ribose-5-phosphate

Question 49

Which cofactor or functional group within the context of the nitrate reductase electron-transport chain has the HIGHEST reduction potential?

A) cysteine
B) NAD⁺
C) FAD
D) molybdenum cofactor
E) cyt b₅₅₇

Question 50

Which statement does NOT accurately describe a difference between heme b and the siroheme found in nitrite reductase?

A) Siroheme contains larger negative charge than heme b.
B) Siroheme contains no vinyl groups, while heme b does.
C) Siroheme contains tetrahedral carbons in the porphyrin ring, while heme b does not.
D) Siroheme contains four propionate groups, while heme b contains two.
E) Siroheme contains Fe²⁺, while heme b contains Fe³⁺.

Question 51

Which list CORRECTLY arranges nitrogen-containing species from most to least oxidized?

A) NO₃^- > NO₂^- > NH₄⁺ > N₂
B) NO₃^- > NO₂^- > N₂ > NH₄⁺
C) NO₂^- > NO₃^- > NH₄⁺ > N₂
D) N₂ > NO₂^- > NO₃^- > NH₄⁺
E) NO₂^- > NO₃^- > N₂ > NH₄⁺

Question 52

Which reaction step in the synthesis of proline is nonenzymatic?

A) the phosphorylation of the side chain
B) the reaction that generates an aldehyde product
C) the cyclization step
D) the reaction that releases inorganic phosphate as a product
E) the reaction that converts a double bond to a single bond

Question 53

Which statement is TRUE regarding the regulation of nitrogen fixation?

A) High concentrations of ADP will activate nitrogen fixation enzymes.
B) Elevated concentrations of ammonia will reduce expression of genes associated with nitrogen fixation.
C) ATP acts as a negative allosteric effector for nitrogenase.
D) Nitrogenase is regulated via adenylylation.
E) Oxygen acts as an allosteric effector for the nitrogenase complex.

Question 54

What high-energy structure is found as part of the major intermediate in the glutamine synthetase reaction?

A) a phosphoanhydride bond
B) a phosphoester
C) an acyl phosphate
D) an enol
E) a thioester

Question 55

Phosphocreatine is derived from which amino acid?

A) alanine
B) arginine
C) cysteine
D) serine
E) lysine

Question 56

Which statement is FALSE regarding the proposed mechanism for glutamine amidotransferases?

A) Part of the mechanism includes the formation of a thioester to a cysteine.
B) A hydrolysis reaction releases glutamine from the active site.
C) Ammonia is released from one substrate before reacting with the second substrate.
D) Phosphorylation is often used to activate the substrate accepting the amino group.
E) Two portions of the enzymes are connected by an "ammonia channel."

Question 57

Which statement is FALSE regarding ladderanes?

A) Ladderanes are classified as phospholipids.
B) Ladderanes are associated with annamoxosomes.
C) Ladderanes are amphipathic membrane components.
D) Ladderanes have less conformational flexibility than equivalent fatty acids.
E) None of the statements is false.

Question 58

Which statement is NOT a similarity in the synthesis of isoleucine, valine, and leucine?

A) Pyruvate is the starting compound for synthesis of all these amino acids.
B) Pyridoxal phosphate is a required cofactor in the synthesis of all these amino acids.
C) These are all essential amino acids in humans.
D) An $\alpha$ -keto acid is the immediate precursor for all three synthetic pathways.
E) Acetyl-CoA is required as a substrate in all three synthetic pathways.

Question 59

In the synthesis of serine from 3-phosphoglycerate, which answer lists the CORRECT order and type of reactions?

A) reduction, hydrolysis, transamination
B) oxidation, transamination, hydrolysis
C) reduction, transamination, hydrolysis
D) oxidation, hydrolysis, transamination
E) hydrolysis, transamination, reduction

Question 60

Which drug is NOT chemotherapeutic?

A) Azaserine
B) Allopurinol
C) Fluorouracil
D) Methotrexate
E) Acivicin

Question 61

In purine biosynthesis, which ring nitrogens are contributed by the sidechain of glutamine?

A) N1 only
B) N1 and N3
C) N1, N3, and N9
D) N1 and N9
E) N3 and N9

Question 62

Which statement is TRUE regarding the conversion of UTP into CTP by cytidylate synthetase?

A) Glutamate is also a substrate for this reaction.
B) This reaction consumes one phosphoanhydride bond.
C) This enzyme is an isomerase.
D) Ammonia is a substrate for the overall reaction.
E) Folate is a required cofactor for the reaction.

Question 63

Which statement is FALSE regarding aspartate transcarbamoylase (ATCase) in prokaryotes?

A) This enzyme catalyzes the rate-limiting step in cytidine biosynthesis.
B) This enzyme is inhibited by pyrimidine triphosphates.
C) Aspartate is a homotropic activator for ATCase.
D) CTP is a heterotropic inhibitor for ATCase.
E) ATCase is regulated by product inhibition.

Question 64

Show the steps by which an intermediate of glycolysis can be converted into serine.

Question 65

Give the name and structure of the glycolytic or citric acid cycle intermediate that has the same carbon skeleton as (a) alanine, (b) glutamate, (c) aspartate.

Question 66

Which process below is NOT required in the conversion of dCTP into dTTP?

A) deamination
B) methylation
C) phosphate hydrolysis
D) phosphate addition
E) reduction

Question 67

Show the reaction catalyzed by glycine synthase, indicating the role of any cofactors that participate.

Question 68

Describe two types of regulation of the enzyme glutamine synthetase and explain why the regulation of this enzyme is so complex.

Question 69

Which molecule does NOT require 5-phosphoribosyl-1-pyrophosphate (PRPP) as a substrate for biosynthesis?

A) adenosine monophosphate
B) cytidine monophosphate
C) guanosine monophosphate
D) histidine
E) All of these molecules require PRPP for biosynthetic pathways.

Question 70

Which statement is TRUE regarding Class I ribonucleotide reductase?

A) The $\beta$ subunit contains the regulatory sites for the enzyme.
B) The $\alpha$ subunit contains the active site cysteines.
C) The $\alpha$ subunit contains the binuclear iron center.
D) This enzyme catalyzes a hydrolysis reaction.
E) ATP is an inhibitor for most isoforms of this enzyme.

Question 71

In bacteria, the amino acids listed below can be derived directly or indirectly from serine, alanine, aspartate, glutamate, or chorismate. Indicate below which of these "parent" compounds provides the carbon skeleton for each amino acid:
Parent compound
Asparagine
__________________
Tryptophan
__________________
Glycine
__________________
Methionine
__________________
Threonine
__________________
Cysteine
__________________
Proline
__________________
Isoleucine
__________________
Phenylalanine
__________________

Question 72

Give the overall reaction that results from the combined action of glutamate synthase and glutamine synthetase.

Question 73

Degradation of purines in primates leads to the formation of what major excreted product?

A) allantoin
B) ammonia
C) hypoxanthine
D) urea
E) uric acid

Question 74

Why is it necessary to have protein in our (human) diets?

Question 75

Show the biosynthetic pathway for the conversion of a citric acid cycle intermediate into proline. Indicate where any cofactors participate.

Question 76

Give the equations for the two-step reaction sequence catalyzed by glutamine synthetase.

Question 77

An animal cell is capable of converting alanine into serine. What is the shortest pathway using known enzymes by which this conversion could be accomplished? Show intermediates and cofactors; no enzyme names are required. (Hint: The first step is removal of the nitrogen by transamination.)

Question 78

Show the two-step reaction catalyzed by tryptophan synthetase.

Question 79

Trace the path of nitrogen from atmospheric N₂ into glutamate. Name the intermediates (no structures necessary) and enzymes, and show any coenzymes involved.

Question 80

Describe and contrast, with diagrams, concerted (cumulative) feedback regulation and sequential feedback inhibition.